Question

我遇到了这个例子（"Hacking Secret Ciphers with Python"，p135），我很困惑：

not (False and True)

该示例表明它的计算结果为False，但我不明白为什么。如果括号修改优先级，那么我们肯定正在评估：

not (False)

哪个评估为True，不是吗？或者我错过了什么？

＆＃13;

// output functions are configurable.  This one just appends some text
// to a pre element.
function outf(text) {
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}

// Here's everything you need to run a python program in skulpt
// grab the code from your textarea
// get a reference to your pre element for output
// configure the output function
// call Sk.importMainWithBody()
function runit() {
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    read: builtinRead
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}

＆＃13;

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.0/jquery.min.js" type="text/javascript"></script>
<script src="http://www.skulpt.org/static/skulpt.min.js" type="text/javascript"></script>
<script src="http://www.skulpt.org/static/skulpt-stdlib.js" type="text/javascript"></script>

<h3>Try This</h3> 
<form>
  <textarea id="yourcode" cols="40" rows="10">print(not (False and True))
  </textarea>
  <br />
  <button type="button" onclick="runit()">Run</button>
</form>
<pre id="output"></pre> 
<!-- If you want turtle graphics include a canvas -->
<div id="mycanvas"></div>

＆＃13;

Answer 1

这实际上涵盖在the errata：

中

，交互式shell应如下所示：
>>> not False and False # not False evaluates first 
True 
>>> not (False and False) # (False and False) evaluates first 
False 
（感谢Omer Chohan）

已在the online version of the chapter中更正，但不在PDF中。

Answer 2

not (False and True)绝对是True，您可以看到在Python REPL中键入表达式。谁声称它是False？

评估不是（假和真）＆＃39;

2 个答案: